The invention relates to a testing apparatus for a leadless package containing a high-frequency integrated circuit chip intended to permit the transmission of signals from n input/output contacts of the package to measuring apparatus by means of high-frequency lines having a given characteristic impedance.
The invention is used in the field of the manufacture of high-frequency integrated circuits.
The term leadless package is to be understood to mean that type of package or envelope better known by those skilled in the art under the designation of "leadless chip carrier". These packages have the property that they can be soldered directly to a peripheral printed circuit by surface mounting. Thus, the wire connections can be dispensed with, which are incompatible with the high-frequency technologies. On the other hand, these packages offer good protection for the integrated circuit chips while maintaining an excellent quality level of the circuits in the case in which they operate in the high-frequency field.
However, before being mounted on a printed circuit board, the leadless package containing the integrated circuit chip must be tested.
Now this operation can be carried out only with great difficulty due to the fact that no leads are present. This operation is further complicated in the case of high-frequency circuits due to the fact that the signals must be transmitted through high-frequency lines having a given characteristic impedance.
On the other hand, there is nowadays a demand among the users for a testing apparatus adapted to each specific circuit. Thus, the manufacturers of integrated circuits have to present in their catalogs this type of testing apparatus, while the circuit designers have to provide for testing apparatus which are marketable, i.e. of a type for a wide public, of simple and inexpensive construction, and also for the circuits themselves.
A testing apparatus for an integrated circuit chip is known from Patent JP-55 72 876 (A) (Fujitsu K.K.). This known apparatus comprises two parts. The first part is constituted by a thick plate of an elastic material, on which a simple conductor circuit is printed, whose geometry permits connecting very compact contacts, which are the image of the input/output contacts of the integrated circuit chip, to conductor contacts of large surface area, which are distributed along the periphery of this elastic plate. The second part is constituted by a rigid socket provided at its central part with a guide hole intended to receive the integrated circuit chip, this hole having a depth smaller than the thickness of the chip. This socket is moreover provided with conductor terminals, of which the geometrical distribution coincides with that of the conductor contacts of large surface area arranged along the periphery of the elastic plate.
The positioning of the chip in such a manner that the circuit faces the exterior in the guide hole of the socket and the pressure of the elastic plate with the conductive surface towards the circuit on the assembly of socket and chip permits establishing the contact between the input/output contacts of the integrated circuit chip and the terminals of the conductors fixed in the rigid socket.
Use of the apparatus described in the aforementioned document therefore consists of connecting an integrated circuit chip directly through an ordinary circuit to measuring apparatus for carrying out the test of the circuit. However, the field of use is not the high-frequency field. The connection conductors which are printed on the thick elastic plate are of the simple conductor type and also of great length, which is incompatible with the transmission of high-frequency signals. This plate has besides its elastic properties no specific dielectric properties. On the other hand, the conductors whose end appears in the rigid socket are not high-frequency lines. None of the elements described in this document provides the possibility of variation, which would permit the transposition to the high-frequency field, while the pure and simple use of such an apparatus is absolutely impossible in this field of use.
Further, the problem solved by the apparatus described in the aforementioned document does not relate to an integrated circuit chip already mounted in a leadless package.